Moisture measuring and selective dryer control system



Nov. 2, 1965 HUFFMAN 3,214,845

MOISTURE MEASURING AND SELECTIVE DRYER CONTROL SYSTEM Filed May 24. 1961IuvEM'ran iNil IA. Huffman ATTORNEY United States Patent Ofi ice3,Zl4%,8i5

Patented Nov. 2, 1965 3,214,345 MOISTURE MEAURWG AND SELETWE DRYERCONTROL SYSTEM Neil A. Huffman, Birmingham, Ala., assignor to industrialNucleonics Corporation, a corporation of Cthio Filed May 24, 1961, Ser.No. 112,347 5 Claims. (Cl. 34-48) This invention relates to measuringand controlling systems utilized in process manufacturing andparticularly to method and means for correcting the moisture profiledrying in the manufacture of fibrous materials.

In a typical industrial process such as a wallboard or hardboard sheetmaking process, the essential steps are the preparation of the pulpmaterial in a form which will permit the formation of a continuous sheetof material; the formation of the sheet, such as on a screen or wire;coarse removal of moisture from the resulting sheet of fibrous material;and the final moisture removal sections. More specifically, hardboardmaterial is produced on a paper-type machine with a head box and aFourdrinier dryer. From the headbox the mat which is approximately oneinch thick enters into a couple of rolls which act as presses to form amat approximately thick. The material then moves along a conveyor whereit is cut into 12 foot lengths and on into an oven where it passesthrough for about one and one-half hours to drive out the remainingmoisture. At a point after the presses the sheet is approximately 50 to55% moisture; and after the sheet leaves the oven, it has approximatelyto moisture.

The oven is generally heated with gas burners and, due to openings alongboth sides thereof, the temperature in the center is considerably warmerthan along the edges where cool air may enter. For this reason, amaterial of uniform moisture content entering the oven would dry outconsiderably more in the middle than on the edges. Depending upon thetime the material was left in the oven, one of two things would happen:either the material would come out of the oven with the edges wet andthe center dried correctly, or the edges would be dried correctly andthe center would be over-dried, or perhaps even burned. It is ofimportance, therefore, that the operator know what the moisture profileis across the sheet of material prior to its entry into the oven. If themoisture profile is known, the heat load can be manually distributed inthe oven to correspond to the edges of the sheet or conversely, themoisture in the sheet material may be adjusted to conform to the heatload through the ovens. Manual control, however, is never suificientlyaccurate for modern day industrial processes. Furthermore, in thisparticular process the moisture across the profile of the sheet is notuniform and is continually varying. Therefore if the moisture profile ofthe sheet were calculated it would in all probability be changed by thetime manual adjustment were made.

The present invention teaches the drying of headboard sheet materialthat overcomes the problems mentioned above. The preferred embodiment isoperative in combination with the oven section of the machine in such away that the control of the oven heaters is continuously matched for themoisture condition existing in the profile of the material produced. Theheaters in the oven section are selectively controlled at that portidnof the width of the material requiring more or less drying beingproduced. In this way the moisture content across the entire width ofthe sheet material is controlled to produce a sheet of uniform moistureas it passes from the oven section.

It is accordingly a primary object of the present invention to provide anew and improved method and means of controlling the moisture dryingprocess in the formation of hardboard sheet material.

it is another object of the present invention to control the moisturedrying process in the formation of hardboard sheet material by theselective control of the final drying section.

It is a further object of the present invention to provide method andmeans of controlling the moisture drying process in the formation ofhardboard sheet material that is readily adaptable with little or nochanges to the conventional processes.

Other objects and features will become apparent from the followingdetailed description of my invention taken in conjunction with thesingle figure drawing showing a preferred embodiment as adapted to aconventional hardboard sheet material process.

Referring now to the figure, in the hardboard sheet material makingprocess the sheet of material 10 emerges from a dryer section it?comprising the drums 17 and 18. The paper passes into an oven mountinglocal upper heating devices 31a, 31b, 31c, 31d, and 31a, and lowerheating devices 32a, 32b, 32c, 32d, and 32a, spaced laterally across thewidth of the hardboard sheet 10. The sheet prior to entering the ovenpasses through a measuring apparatus 11 comprising moisture responsiveelements 12 and 13. The measuring apparatus 11 is so disposed relativeto the moving sheet of material that it may be traversed laterally toobtain information on the relative moisture content at all points acrossthe width of the sheet of moving material. A number of devices aresuitable for this detector. One of these is a beta radiation absorptiongauging system disclosed in US. Patent 2,909,660. In this instance, thevariations in indicating the mass per unit area across the width of thesheet of paper may be interpreted to be the result of moisture contentvariations. Another means of performing this measurement is a dielectricmeasuring apparatus which is responsive to changes in the capacitance ofthe measured material as it is traversed across the width. Preferablythe moisture measuring system most ideally suited to my invention isthat disclosed in Serial No. 41,975 filed July 11, 1960, now Patent No.3,155,900, for Measuring System. In that system the variations in theresulting signal from the measuring device are again interpreted toresult from variations in the moisture content independent of mass atvarious points across the width of the sheet of material. Thisinterpretation is based on the fact that variations in moisture contentcontribute of the order of 40 times as .much variational signal to thedetector output as would corresponding variations in the amount of pulpmaterial in the sheet. Numerous other detecting devices could be adaptedfor this use; among them, those depending on infrared reflectance andabsorptivity. It is to be emphasized here that the output of themoisture responsive device does not have to be of any particularaccuracy with regard to absolute readings of the value of moistureexisting at any one region of the sheet. Rather, all that is required isthat the detecting device be able to signal what regions of the sheethave an average moisture content greater or less than other regions.

A readout of the indications of the moisture responsive detector isshown in the recorder apparatus 19 which contains the scale 20 on whichthe width of the sheet of paper has been arbitrarily divided into theregions 20a, 20b, 20c, 20d, and Ztle. The marking device 21 which may bethe recording pen of a selfbalancing X-Y potentiometer traces theindication of the profile data developed by the measuring device 11. Thetrace 22 is represented to occur at a later time than the trace 23.Traces 22 and 23 represent sequential recordings of the output of themoisture responsive detector in its sequential traverses across thewidth of the sheet of paper. Regions a, 20b, 20c, 26d, and 20ecorrespond, therefore, to regions of the sheet 10a, 10b, 10c, 10d, and10e. Alternatively, the recording system illustrated in U.S. Patent No.2,909,660 to Frank Alexander may be adapted to indicate moisture readingwith profile position.

The output of the recorder 19 is fed to a computer 33 whereas in turnthe output of the computer 33 is applied to the heater controller 35.This controller selectively actuates one or more of the auxiliaryheating devices mounted on the frame 14, and shown as upper heaters 31a,31b, 31c, 31d, and 31s, and lower heaters 32a, 32b, 32c, 32d, and 322,mounted transversely to the process. These heating devices may be gasburners in an oven, air jets or other known heating devices that may beselectively controlled.

In operation the moisture responsive device 11 generates profileinformation such as that represented by trace 23. The signal from thecomputer 33 actuates the heaters through the heater controller 35 toapply the proper degree and duration of local heat to the moving sheet.The computer 33 may .be one conventionally available or may simplycomprise circuitry capable of signal comparison and operative to producea voltage for a duration dependent upon the degree of moisturedeviation. Controller 35 also is conventionally known and wouldpreferably be of the proportional type such as that disclosed andutilized in the US. patent to Donald E. Varner, No. 2,895,888.

In the illustration of the preferred embodiment wherein the edges of thehardboard would retain a greater percentage of moisture, the intensityand duration of the heaters 31a, 32a, 31:: and 32e would be greater thanthe heaters in the central area. There may be instances where for somereason or other in the process the moisture content of the sheet as itenters the dryer may have wetter or dryer streaks. Since the moisturecontent is converted into a relative signal the heater in the ovencorresponding to the streak area would be controlled accordingly.

The use of the above cited controlled localized heating of regions inthe oven or final dryer section across the profile of the moving sheetproduces a sheet having a uniform moisture characteristic across itswidth. Accordingly a uniform physical characteristic is imparted to thesheet material and the need of an attendant is eliminated.

Although certain and specific illustrations are given, it will beapparent to those skilled in the art that modifications may be madewithout departing from the true spirit and scope of the invention.

1 claim:

1. In a manufacturing machine for processing a length of a fibrousmaterial, having a drying section having an input side and an outputside with a series of selective drying means spaced across the width ofsaid material, each of said means alfecting the moisture condition ofsaid material at a portion of said width, said portion beingsubstantially less than the total extent of said Width, the improvementof uniformly drying said sheet comprising means for moisture gaugingsaid material, means for mounting said gauging means on said input sideof said drying section, traversing means associated with said mountingmeans for causing said gauging means to scan said material across saidwidth thereof, computer means connected to said gauging means forgenerating a signal indicative of said moisture condition at thetraversing point of measurement, controller means connected between saidcomputer means and said selective drying means for utilizing saidmoisture indicative signal to control the effectiveness of said dryingmeans at the portion of said sheet width corresponding to saidtraversing point of measurement.

2. In a manufacturing machine for processing a length of a fibrousmaterial, having a drying section having an i p t ide and n output sidewit-h a series of selective drying means spaced across the width of saidmaterial, each of said means affecting the moisture condition of saidmaterial at a portion of said width, said portion being substantiallyless than the total extent of said Width, the improvement of uniformlydrying said material comprising, gauging means for determining themoisture across the width of said material, means for mounting saidgauging means on said input side of said drying means, computer meansconnected to said gauging means for generating a signal indicative ofeach of said portions of said material, controller means connectedbetween said computer means and said selective drying means forutilizing said moisture indicative signal to control the effectivenessof said drying means at the portion of said material corresponding tosaid moisture gauged width portion.

3. In a manufacturing machine for continuously processing a laterallyextended length of a fibrous material, having a final drying sectionhaving an input side and an output side with a series of selectivedrying means spaced across the width of said material, each of saidmeans afiecting the moisture condition of said material at a portion ofsaid width, said portion being substantially less than the total extentof said width, the improvement of uniformly drying said materialcomprising means for moisture gauging said material, means for mountingsaid gauging means on said input side of said final drying section,traversing means associated with said mounting means for causing saidgauging means to cyclically scan said material across said widththereof, computer means connected to said gauging means for generating asignal indicative of said moisture condition at the traversing point ofmeasurement, a continuous chart recording means, means for connectingsaid signal to said recorder to indicate the moisture of said materialat any given point of traverse, and controller means connected betweensaid computer means and said selective drying means for utilizing saidmoisture indicative signal to control the effectiveness of said dryingmeans at the portion of said material width corresponding to saidtraversing point of measurement.

4. In a hardboard manufacturing machine having a sheet forming sectionand a final dryer section having an input side and an output side andincluding a plurality of adjustable selective drying means positionedacross said sheet to affect the moisture content of a discrete portionof said sheet width in accordance with the output of said drying means,the improvement comprising means mounted adjacent said input of saidfinal dryer section for determining the variations in moisture acrosssaid sheet entering said final dryer section, and means for adjustingthe output of each of said selective drying means in accordance with themeasured moisture content of said sheet at the discrete portionassociated with said drying means.

5. In manufacturing apparatus for continuously processing a laterallyextended sheet of fibrous material, said apparatus having a final dryersection having an input side and an output side and including a seriesof selective drying means spaced across the width of said sheet, each ofsaid means affecting the moisture condition of said material at aportion of said width, said portion being substantially less than thetotal extent of said width, the improvement for uniformly drying saidsheet comprising means mounted adjacent said input side of said finaldryer sections for measuring the variations in moisture across the widthof said sheet entering said final dryer section, a computer connected tosaid measuring means for generating a signal indicative of thevariations of said moisture from a desired value thereof and controllermeans connected between said computer and said selective drying meansfor utilizing said moisture indicative signal to control theeffectiveness of said drying means at the portion of said sheetassociated with said selective drying means.

(References on following page) References Cited by the Examiner UNITEDSTATES PATENTS References Cited by the Applicant UNITED STATES PATENTSKrogh 34 .4 2,355,391 8/44 Nelson et a1.

Zabel 324 5 5 3,040,807 6/62 Chops.

Haltmeier 3 -48 PERCY L. PATRICK, Primary Examiner.

Alexander 25 (P814 BENJAMIN BENDETT, NORMAN YUDKOFF, Undefhay 34-160Examiners.

4. IN A HARDBOARD MANUFACTURING MACHINE HAVING A SHEET FORMING SECTIONAND A FINAL DRYER SECTION HAVING AN INPUT SIDE AND AN OUTPUT SIDE ANDINCLUDING A PLURALITY OF ADJUSTABLE SELECTIVE DRYING MEANS POSITIONEDACROSS SAID SHEET TO AFFECT THE MOISTURE CONTENT OF A DISCRETE PORTIONOF SAID SHEET WIDTH IN ACCORDANCE WITH THE OUTPUT OF SAID DRYING MEANS,THE IMPROVEMENT COMPRISING MEANS MOUNTED ADJACENT SAID INPUT OF SAIDFINAL DRYER SECTION FOR DETERMINING THE VARIATIONS IN MOISTURE ACROSSSAID SHEET ENTERING SAID FINAL DRYER SECTION, AND MEANS FOR ADJUSTINGTHE OUTPUT OF EACH OF SAID SELECTIVE DRYING MEANS IN ACCORDANCE WITH THEMEASURED MOISTURE CONTENT OF SAID SHEET AT THE DISCRETE PORTIONASSOCIATED WITH SAID DRYING MEANS.